FR2604448A1 - RECLASSIFICATION OF DISTRIBUTION AREAS DEFINED BETWEEN FIXED AUBES OF A TURBINE - Google Patents

Abstract

THE INVENTION CONCERNS THE RECLASSIFICATION OF THE DEFINED DISTRIBUTION ZONES BETWEEN FIXED BLADES OF A TURBINE. WHEN A FIXED VANE 1 OF A GAS TURBINE HAS SUFFERED DEFORMATION AND WEAR, THE GAP BETWEEN SUCCESSIVE FIXED BLADES 6, 7 DEFINING DISTRIBUTION ZONES 8, 9 OF THE GAS FLOW, INCREASES. THE WEAR AREA IS RECHARGED BY APPLYING LAYERS OF A TAPE 12 OF A UNIFORM THICKNESS TO THE DAWN. THIS TAPE INCLUDES A MIXTURE OF A BINDING AGENT AND AN ALLOY POWDER, WHICH IS COMPATIBLE WITH THE SUBSTRATE ALLOY. THE INVENTION IS USED TO REDUCE THE COST OF REPAIRING WASTED FIXED BLADES OF THE TURBINES BY AVOIDING ANY PROCESS OF BENDING OR HOT FORMING.

Description

Reclassification process for defined distribution areas

  between fixed vanes of a turbine.

The present invention relates to

  elements of a gas turbine and, more specifically,

  and a method of reclassifying the defined distribution area between adjacent stationary vanes of a turbine. A gas turbine includes a compressor section, a combustion section, and a turbine section. Inside the turbine section are alternating rows of rotating blades and vanes. As the hot combustion gases pass through the turbine section, the blades are rotated, thereby rotating a shaft that generates a motive force to drive the compressor section and other auxiliary systems. The higher the temperature of the gases, the more the motive force that can be extracted in the turbine section is

  important and the overall efficiency is great.

  In order to increase the thermal capacity under the operating conditions of the turbine section, materials consisting of superalloys based on cobalt and nickel are used to make the blades and vanes

  fixed-bearing surfaces of turbines. These men

  maintain the mechanical resistance to

high temperatures.

  The stationary vanes disposed between the rows of rotating vane stabilize and direct the flow of gas from a row of rotating vanes of a turbine to the next row, a distribution area being defined

  by the spacing between the adjacent stationary vanes.

  This stabilization of the gas flow optimizes the amount of motive force extracted in the turbine section. In general, gas flow distribution zones are assigned

  classification numbers which are in correlation with

  with the volumetric gas flow, thus making it possible to make comparisons concerning the properties defining the gas flows between

  fixed vanes with complex geometry. As a result

  For reasons of convenience, the distribution area is defined in terms of

  dimension being part of a class. For example

  in a gas turbine of a particular model

  Class 27 distribution area has an open area of 12,051-12,219 cm (1,868-1,894 square inches) while a Class 29 distribution area has an open area of 12,38-12,541 cm2 ( 1, 919-1.944 inches

  square), whatever the geometry.

  During commissioning, the surface

  vanes deteriorate as a result of oxidation.

  and erosion of metals resulting from abrasive and corrosive materials present in the flow of the gas stream impinging the vanes. In addition, the high stresses resulting from the gases at high temperatures favor the deformation of the vanes, thereby enlarging the distribution zone with consequent loss of turbine efficiency. During periodic turbine reconditioning, the blades are inspected for physical deterioration and evaluated for the degree of change in the flow zone and the effect produced.

  on the classification of the distribution area.

  Before these blades can be reinstalled

  In the turbine, any eroded material must be replaced and, moreover, the blades must be reclassified. In addition, stationary vanes which have eventually suffered a loss of metal or a change in shape following removal of their coating or

  repairs, must be reclassified.

  There are several methods for modifying a fixed blade to bring the gas flow distribution area back to its original classification (reclassification). One method is to hitting or otherwise bending the trailing edge of the fixed blade, thereby narrowing

  the free space between adjacent fixed vanes.

  However, this bending gives rise to

  those that can cause cracks in the dawn. This bending can also cause

  excessive deformation of the fixed dawn,

  thus to properly adjust and seal the internal cooling tubes, while the fasteners that hold the vanes fixed during bending can

  deform the foot of the blades or crush their base.

  Although the stresses resulting from bending can be reduced, many alloys provided for high temperatures and used in gas turbines can not be shaped or bent hot due to the adverse effects on material properties such as fatigue strength. . Since the bending process does not recharge

  metal on the surface of the dawn, no

  In the case of strength, tribution is made and, from a structural point of view, the blade is less resistant than a new one, thus limiting the service life of this blade.

  Another method for reclassifying

  Proud of stationary turbine blades is to add an alloy to the deteriorated surface of a blade by means of a combined plasma welding / spraying process such as that described in US Pat. No. 4,028,787 to Cretella. et al. This process requires the addition of weld beads to the worn surface to reinforce it, and the addition of a number of layers of the plasma-sprayed alloy to obtain the desired alloy thickness. . -This process requires a lot of work, because a welder must add a number of weld seams on a small surface, then clean the dawn and then,

  add a number of layers of pulverulent

  plasma. In addition, dawn can be damaged due to thermal stresses

  that involves the welding operation.

  Another problem with the plasma welding / spraying process is the specific surface area of deterioration. It is to be expected that the deterioration will be more severe at the narrowest dimension of the distribution area where the speed of the gas flow

  is at its maximum. During the pulping process

  Plasma verification, an alloy is added to the surface in very thin layers, thus defining a wide uniform configuration. At the end

  of plasma spraying, the excess material

  should be removed from the non-eroded areas of dawn. If the deterioration is severe in a specific area, many layers of the alloy must be added and many of them must be removed from the non-eroded areas. This process is time consuming and results in losses in the alloy materials involved. As a result, it has become necessary to find a method to reclassify turbine blades, which involves adding an alloy to a specific surface, while reducing

expenses incurred to a minimum.

  An object of the present invention is to provide a simplified method for adding a controlled amount of an alloy to a surface

specific of an article.

  Another object of the present invention is to provide a method for reclassifying

  turbines, this method makes it possible to

  both to reduce the importance of the work to be performed to reload an alloy at a specific location on the surface of a dawn

fixed turbine.

  Another object of the present invention is to provide a method for the reclassification of stationary vanes of turbines, which can not be

shaped or bent hot.

  These and other objects of the present invention are realized by applying one or more layers of a ribbon material to the specific surface of an article until a desired thickness is obtained. ribbon comprising a mixture of a binding agent and an alloy powder, which mixture is compatible with the substrate, while it is converted into a flexible ribbon of a

  uniform thickness and provided with an adhesive support.

  After application of the ribbon, the article is heated to a temperature at which the adhesive and the binding agent decompose and at which there is also a diffusion between the alloy powder

  contained in the ribbon and alloy of the substrate.

  By using layers of ribbon of constant thickness, a precise reclassification of the gas distribution zone in a specific surface prior to heating can be carried out and without the need for laborious welding or plasma spraying operations.

  reclassification that can be carried out jointly

  with the repair of the superficial parts

  cracks. A final machining step will unite the edges of the ribbon, thus giving a

Smooth profile surface.

  The single appended drawing illustrates the method of reclassifying the blades according to

the present invention.

  This drawing illustrates the method of

  classification of the present invention. A fixed blade 1 comprises a concave surface 2, a convex surface 3, a leading edge 4 and a trailing edge 5. This blade 1 is disposed between an upstream fixed blade 6 and a fixed downstream blade 7, a distribution zone 8 being defined between

  vanes 6 and 1, while a zone of

  FIG. 9 is defined between the stationary vanes 1 and 7, which distribution zones are measured at the narrowest spacing between two adjacent stationary vanes being illustrated by the lines 10, 11, 12 and 13. For the purpose of illustration, it will be assumed that, for the blades 1, 6 and 7, fixed vanes are used which have been inspected and where it has been found necessary to reclassify the distribution zone to obtain an optimum efficiency of the turbine. By way of further illustration, the blades 1, 6 and 7 are made of a cobalt-based superalloy having the following nominal composition: 23.4 Cr,

  1ON, 7W, 3.5Ta, 0.2T, 0.6C, 0.5Zr and 1.5Fe.

  Fixed vanes made of such material can not be struck or bent hot

  without prejudicially modifying the pro-

  fatigue properties of the alloy.

  As a result, these vanes must be replaced or they must be reloaded from an alloy substrate in deteriorated areas. Although a

  such alloy is indicated to illustrate the

  In the present invention, those skilled in the art will appreciate that the method of the present invention could be beneficial for articles made of other materials such as superalloys.

based on iron or nickel.

  Consequently, reclas-

  by adding successive layers of a ribbon material 14 to the deteriorated surface of the fixed vane 1. The ribbon used comprises a mixture of an alloy powder and a binder, which mixture is converted into a paste and spread to form a sheet of uniform thickness. The ribbon material can be obtained by adopting the teachings of U.S. Patent No. 3,293,072, herein incorporated by reference. This patent indicates

  the way you can get a ribbon using

  a removable carrier film as a subsi-

  and employing an organic polymer such as polyvinyl alcohol or polymethacrylates, together with a smaller amount of a volatile plasticizer such as sucrose aceto-isobutyrate, dibutyl phthalate or diethyl oxalate, when it is a use with polymethacrylate binders, and glycerine when it comes to using

  with binders based on polyvinyl alcohol

  than. The powdery material is converted into a slurry with the binding agent, the plasticizer and the acetone as a solvent, this slurry being applied in a thin layer on a support

  removable, then heated to remove the solvent.

  The sheet of material obtained is then cut

  in flexible bands to which we add a

adhesive port.

  The alloy powder constitutes the

  it is compatible with the substrate while it can withstand the conditions of the ambient environment for commissioning; it usually comprises a compatible alloy that can be bonded by brazing or by

  diffusion. When it comes to using the super-

  cobalt-based alloy described above, the alloy powder comprises a mixture of 60% by weight of an alloy whose nominal composition is 24.5Cr, 40Ni, 3B, the remainder being cobalt,

  as well as 40% by weight of the alloy of the

in the form of a powder.

  Referring to the accompanying drawing, the tape 14 provided with an adhesive backing is added in layers until the desired amount of alloy is obtained. Since this ribbon is thin and flexible, it is easy to adapt it specially to the desired shape and thickness, having the possibility of marrying the contour of irregular surfaces. The layers are deposited in a pyramid to form a progressive rise in the thickness of the alloy in

  a specific surface of the fixed blade, shrinking

  thus, the space between the vanes.

  Between the vanes 6 and 1,

  felt four layers of ribbon while between

  the vanes 1 and 7, two layers are observed.

  Those skilled in the art will understand that the tape can be applied to one or both sides of the fixed blade, depending on the circumstances

particular cases.

  The fixed dawn 1 on which was applied

  ribbon 14, is then heated to a

  temperature at which a bond occurs.

  At this temperature or at a lower temperature, the binding agent and the adhesive support decompose without leaving important residues, thus avoiding contaminating the alloy. The alloy powder contained in the ribbon then binds to the alloy of the substrate, thereby forming a continuous microstructure free of voids. In a preferred embodiment, this bond involves a transient liquid phase bond as disclosed in U.S. Patent Nos. 3,678,570, 4,005,988, and 4,073,639, incorporated herein by reference, thereby establishing a bonding to a temperature at which the base alloy can be exposed without any deleterious effects occurring. During the transient connection in the liquid phase, the article is maintained at the bonding temperature up to

  obtaining isothermal solidification.

  To obtain a transient connection in the liquid phase, the alloy of the ribbon contains the same base metal as the fixed superalloy blade and has a high boron content. The presence of boron, preferably 1-5% by weight, serves as a melting point lowering agent, thereby bringing the melting point temperature below that of the superalloy, as well as below that of the superalloy. which would cause harmful and irreversible metallurgical changes in the substrate alloy. After bonding, the fixed blade is subjected to a heat treatment to ensure the homogenization of the microstructure

  between the alloy of the ribbon and the alloy of the substrate.

  After binding the ribbon to the fixed dawn,

  the surface is machined to obtain the super-profile

  correct software. For this operation, it is usually necessary to join the edges of the ribbon

  to obtain a smooth aerodynamic surface.

EXAMPLE

  A fixed turbine blade consisting of a cobalt-based superalloy and having the following nominal composition was removed: 23.4Cr, 1ONi, 7W, 3.5Ta, 0.2Ti, 0.6C, 0.5Zr and 1 , 5Fe, and examined after a number of hours of operation in a gas turbine. This blade was cleaned by shot blasting and an aluminide coating was chemically removed from its surfaces. The dawn was then examined with fluorescent penetrating material such as "Zyglo" (registered trademark) to locate crevices or other superficial defects. After determining that deficiencies could be corrected, the distribution area (class) was measured and recorded. It was determined that the area of distribution had increased and that a supply of material was needed to

  bring back the dawn to its initial class.

  The fixed cobalt alloy blade was cleaned in a hydrogen retort at a temperature of 1,149 C (2,100 F) for two and a half hours, then it was cleaned under

  empty at 1.149 C (2.100 F) for 2 hours.

  On the blade was then applied a ribbon material having a uniform thickness of 0.508 mm (0.020 inch) and containing an alloy powder that was compatible with the alloy of the substrate and a binder, the mixture formulated to assure a transient connection in the liquid phase consisting of a mixture of 60% by weight of an alloy having the following nominal composition: 24.5Cr, 40Ni, 3B, the balance being cobalt, as well as 40% by weight of the alloy of the substrate in the form of a powder. We have

  cut four layers of ribbon to the appropriate shape

  requested and, using an adhesive, they were applied

  on one side of the dawn, while one

  applied two layers on the trailing edge.

  The width of each layer was varied to promote regular charging of the material on the surface of the blade. This was then heated to a temperature of 1149 ° C. (2.100 ° F.) under vacuum and maintained at this temperature for 12 hours. At this temperature, the binder and the adhesive support decompose leaving essentially no residue, while the molten alloy powder fuses to and diffuses into the alloy of the substrate, thereby defining a unitary thickened surface, the ribbon material at the same time filling any crevices present in the area being reclassified. The solidification takes place isothermally as the boron-based agent lowers the melting point.

diffuses into the alloy of the substrate.

  Next, the material refill is joined using an abrasive belt grinding wheel that cuts the edges of the ribbon decreasing to obtain a smooth and continuous surface. Next, the blade is shot blasted, examined with fluorescent particles, and the dispensing area is measured to confirm proper reclassification. The air holes, which may be obstructed in the dawn, are re-opened and a coating is applied again.

on this one.

  The coated dawn is subject to an examination

  final and its classification is checked again.

  It should be noted that the coating generally

  as a consequence of bringing dawn into a classi-

  lower density due to the greater thickness of the deposited coating material

  on the surface defining the distribution area.

  This factor must be taken into account when

  it's about determining the layers of ribbon

which must be applied.

  By adopting a reclassification process

  using a ribbon, very laborious welding operations are

  the thermal stresses that result.

  This method also makes it possible to reload in a controlled manner at a precise fixed value and to obtain a homogeneous configuration of the alloy of the substrate. Although the preferred embodiment of the present invention has been described

  by referring to a fixed turbine blade, the man

  It will be appreciated by those skilled in the art that the present invention may be beneficial to any turbine element requiring a controlled supply of

  substrate alloy on a specific surface.

  Although the description was given in

  Referring to a cobalt-based superalloy at a temperature of 1,149 C (2,100 F) and at a time of 12 hours, those skilled in the art will understand that other modifications, in terms of time, temperature, alloy , thickness or ribbon width, can be considered without

  depart from the scope of the present invention.

Claims (11)

  A method of reloading a specific surface of a metal article by means of a controlled amount of an alloy, characterized in that it comprises the steps of applying one or more layers of a ribbon material on the specific surface and until a desired thickness is obtained, this tape comprising a mixture of a binding agent and an alloy powder, this mixture being compatible with the alloy of the substrate, after which it is made into a ribbon of uniform thickness with an adhesive backing; and heat the item to a temperature   to which the adhesive and the binding agent decompose   pose, and to which also a bond occurs between the contained powdered alloy   in the ribbon, and the alloy of the substrate.   2. Method according to claim 1, characterized in that the article and the ribbon are heated under vacuum.   3. Method according to claim 1, characterized in that the connection consists of a broadcast link.   4. Method according to claim 1, characterized in that the ribbon provided with its layers is united to obtain a smooth profiled surface. 5. Method according to claim 1, characterized in that the aforementioned connection is   a transient connection in the liquid phase, the   binding of the tape comprising between 1 and 5% by weight of boron.   6. Process according to claim 5,   characterized by comprising the steps of   of keeping the article at the temperature   until the solidification iso-   therme takes place; and subject the article to heat treatment to ensure homogenization of   the alloy of the ribbon and the alloy of the substrate.   7. A method of reclassifying the distribution zone comprised between adjacent stationary vanes of turbines, characterized in that it comprises the steps of: determining the excess spacing between the vanes fixed in the distribution zone, applying until a desired thickness is obtained, one or more layers of a ribbon material on the defective surface, the ribbon comprising a mixture of a binder and an alloy powder, which is similar to the alloy of the substrate, which mixture is then converted into a ribbon of uniform thickness comprising an adhesive support; to heat the fixed dawn to a temperature   to which the adhesive and the binding agent decompose   and to which there is also a bond between the alloy powder contained in the ribbon and the alloy of the substrate; and unite the added alloy material to   obtain an essentially smooth surface.   8. Process according to claim 7, characterized in that the fixed blade is heated and the vacuum ribbon.   9. Process according to claim 7, characterized in that this connection consists in a broadcast link.   10. The method of claim 7, characterized in that this connection consists of a transient connection in the liquid phase, the alloy of the tape comprising between 1 and 5% by weight of boron. 11. The method of claim 10,   characterized by comprising the steps of   further comprising: maintaining the blade constant at the bonding temperature until isothermal solidification occurs; and   subject dawn to a heat treatment   to ensure the homogenisation of the   bonding of the ribbon and alloy of the substrate.